Catechins are known to have a cholesterol-suppressing effect and an α-amylase activity inhibitory effect (Patent Documents 1 and 2). In order to obtain such physiological effects, an adult is required to drink four to five cups of tea a day. So there has been a demand for the development of a technology designed to incorporate catechins at a high concentration in beverages in order to facilitate the ingestion of a large amount of catechins. One of such methods is to add catechins in a dissolved form to a beverage by using a concentrate of a green tea extract (Patent Document 3) or the like.
In order to extract catechins having a stable taste from green tea, semi-fermented tea or fermented tea leaves, there are methods known as the two-stage extraction method in which extraction is performed with low-temperature water, followed by extraction under elevated temperature; and the extraction method to be performed in strong acidity (Patent Documents 4 to 6). The capability of such extraction methods, however, is limited to extracting catechins from tea leaves, and they are also intended only to stabilize the taste of a purified product and maintain a good taste.
Catechins are usually known to be sparingly soluble in an organic solvent, and their extraction can be accelerated under the weakly acidic conditions. Nonetheless, catechins have a problem that could lead to a critical decline in extraction efficiency when the proportion of an organic solvent is increased (Patent Document 7).
Not only does a tea leaf contain about 15 mass % of catechins, but it also contains caffeine in an mount of from 2 to 4 mass %. Caffeine has a central nervous stimulating activity and therefore can be used for warding off drowsiness. On the other hand, caffeine is said to have harmful effects such as jitteriness, vomiting and sleeplessness, if excessively used. Methods of selectively removing caffeine from a caffeine-containing composition have been investigated. Examples of such methods include a method in which caffeine is removed from coffee by bringing the coffee into contact with a caffeine adsorbent such as active carbon under atmospheric pressure of from 120 to 250 (Patent Document 8) and a method in which caffeine is selectively removed by bringing an aqueous solution containing caffeine into contact with active clay or acid clay (Patent Document 9). The former method, however, lacks simplicity in terms of the applicability on an industrial scale, because this method is related to a supercritical extraction technology and imposes a huge burden on its equipments during the process. Furthermore, there is a problem that although caffeine may be removed selectively by this method, it also brings noxious changes to the construction of catechins serving as an effective ingredient. The latter method, meanwhile, is accompanied with the problem that caffeine can be removed selectively only by using active carbon or acid clay, but the beverage thus obtained may have a deteriorated color.    [Patent Document 1] JP-A-60-156614    [Patent Document 2] JP-A-3-133928    [Patent Document 3] JP-A-59-219384    [Patent Document 4] JP-A-2003-219799    [Patent Document 5] JP-A-2003-219800    [Patent Document 6] JP-A-2003-225053    [Patent Document 7] JP-A-2004-147508    [Patent Document 8] JP-A-53-18772    [Patent Document 9] JP-A-6-142405